Greenhouse Gases/Effect

Greenhouse Gases (GHG's) are the various gases that block outgoing long-wave infrared from easily leaving our atmosphere. The Greenhouse Effect (GHE) is the physical mechanism of this blocking mechanism in our atmosphere that influence how much heat we retain within the atmosphere.

Greenhouse Gases - CO2, H20, CH4, N2O

Simply put, without greenhouse gases, or the greenhouse effect, Earth would be a frozen planet, incapable of sustaining life as we know it. There would be no plants, no trees, no animals, just frozen ice and stone.

We need greenhouse gases to capture and hold heat from the sun. Not enough greenhouse gases and we are in an ice age. Too much greenhouse gases and we are in the age of the dinosaurs, or worse. Greenhouse gases are essential sustain the planet as we now know it.

The dominant natural greenhouse gases are H20 (water), CO2 (carbon dioxide), CH4 (methane), and Nitrous oxide (N2O). There are also industrial CFC's (Chlorofluorocarbons). H20, CO2, CH4, and N2O are all naturally present in the the atmosphere. Chiefly, these gases and the ones that keep us warm enough to live relatively comfortably here on Earth. This is the "natural" greenhouse effect.

The natural forces imposed on our climate system, such as the external forcing of the sun and the Milankovitch cycles, and the internal responses of the climate system control the amount of warmth we enjoy.

The main concern today is that, by the burning of fossil-fuels and other activities, humans increasing the abundance of greenhouse gases in the atmosphere, contributing to an enhanced greenhouse effect. This enhanced greenhouse effect is not natural.

Greenhouse Gases

The National Academy of Sciences, National Research Council, Board on Atmospheric Science and Climate Present 'Climate Change: Lines of Evidence - Greenhouse Gases'

Understanding what it means to add greenhouse gases:

If you need to go somewhere in your car, you need to add gas. Your measure of distance is MPG (Miles per Gallon) or KPL (Kilometers per Liter). The same applies to temperature in our atmosphere. The atmosphere is the tank. The more gas you add, the more distance you can travel. The difference is that in this case the distance is temperature, not miles.

Commentary from Andrew Lacis re. Lacis et al 2010

From NOAA/NCDC

What is the greenhouse effect, and is it affecting our climate?

The greenhouse effect is unquestionably real and helps to regulate the temperature of our planet. It is essential for life on Earth and is one of Earth's natural processes. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they effectively 'trap' heat in the lower atmosphere) and re-radiation downward of some of that heat. Water vapor is the most abundant greenhouse gas, followed by carbon dioxide and other trace gases. Without a natural greenhouse effect, the temperature of the Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C). So, the concern is not with the fact that we have a greenhouse effect, but whether human activities are leading to an enhancement of the greenhouse effect by the emission of greenhouse gases through fossil fuel combustion and deforestation.

The Greenhouse Effect (GHE)

The greenhouse effect is the process, or mechanism, by which greenhouse gases interfere with the direct radiation of heat energy leaving the surface of the planet. In other words GHG's can get in the way of heat escaping, and thus prevent some of the heat from escaping quickly, or easily. When heat energy hits a greenhouse gas molecule it can re-radiate in any number of directions. Some energy radiates back down and some at angles to interact with other molecules.

Eventually, heat energy makes it back out to space. The amount of greenhouse gases in the atmosphere combined with other factors determine the radiative balance, and/or temperature at which relative thermal equilibrium for a planet occurs based on these factors.

How do we know CO2 is a greenhouse gas?

What are the major contributors to the greenhouse effect?

Estimating precisely what the contributions are to the effect is complicated by many factors. Spectral overlap, altitude, changing coverage that must be calculated based on averages. However, while getting precise numbers is difficult approximate numbers are beginning to come into focus in a more reliable way.

Gavin Schmidt et al. and Andy Lacis et al., have both had papers published in 2010 that seem to have corralled the effects into general areas with reasonable attribution. Here is what it generally breaks down to: